Control systems in various contexts have become extremely complex and constitute a major cost item. One example arises in the environment of a factory such as a paper mill in which many devices such as motors, valves, etc., are controlled from a central control room. It has previously been necessary to run a set of wires from each switch, pushbutton or the like in the control room to each device in the field in order to be able to control that device independently of other devices. The result is that the number of wires in a factory of significant size can easily be in the thousands. The cost of the copper or other metal is obviously enormous and the labor to install such a system is even greater. In addition, the conduits to hold the wires can total several square feet in cross section, and if a problem arises in the wiring the task of locating and repairing or replacing the offending wire or wires is extremely difficult.
Another example is found in the modern automobile. Each controllable electrical device in an automobile requires that a wire, or a pair or wires, be run from the location of the device to the dashboard or other control location. The more such devices there are, the more complex the problem, but even on the simplest vehicles produced today, the wiring harnesses which are needed are large, complicated, expensive and heavy, not only adding to the initial cost of the vehicle but also reducing its fuel efficiency.
Recent efforts have been made by various inventors, notably employees of automotive companies, to develop multiplex systems which use a small number of wires, compared with the traditional systems, to accomplish the necessary control. The systems developed thus far, however, appear to have two major disadvantages, cost and complexity. In addition, it does not appear that previously developed systems can operate in a "noisy" environment with the kind of reliability which must be guaranteed in an automotive context as well as in many industrial environments. The noise referred to in this context is, of course, electrical rather than acoustic noise.